In daily use, a stool or a ladder is used to take objects at high place or to disassemble or assemble the electric apparatus at high place. The stool is not stable to stamp, it is dangerous. A ladder unable to fold up has large size, so that it is inconvenient for storage and moving. However, the rung of existing folding ladders is usually directly movably hinged to the front legs and the rear legs, thus making it not flexible to fold up, the rung may be locked during being folded or unfolded.